Fluid extraction system, lithographic apparatus and device manufacturing method

ABSTRACT

An immersion lithographic apparatus typically includes a fluid handling system. The fluid handling system generally has a two-phase fluid extraction system configured to remove a mixture of gas and liquid from a given location. Because the extraction fluid comprises two phases, the pressure in the extraction system can vary. This pressure variation can be passed through the immersion liquid and cause inaccuracy in the exposure. To reduce the pressure fluctuation in the extraction system, a buffer chamber may be used. This buffer chamber may be connected to the fluid extraction system in order to provide a volume of gas which reduces pressure fluctuation. Alternatively or additionally, a flexible wall may be provided somewhere in the fluid extraction system. The flexible wall may change shape in response to a pressure change in the fluid extraction system. By changing shape, the flexible wall can help to reduce, or eliminate, the pressure fluctuation.

This application claims priority and benefit under 35 U.S.C. §119(e) toU.S. Provisional Patent Application No. 61/193,639, entitled “FluidExtraction System, Lithographic Apparatus and Device ManufacturingMethod”, filed on Dec. 11, 2008. The content of that application isincorporated herein in its entirety by reference.

FIELD

The invention relates to a fluid extraction system, a lithographicapparatus and a method for manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe invention will be described with reference to liquid. However,another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

Submersing the substrate or substrate and substrate table in a bath ofliquid (see, for example, U.S. Pat. No. 4,509,852) means that there is alarge body of liquid that must be accelerated during a scanningexposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

In an immersion apparatus, immersion fluid is handled by a fluidhandling system, structure or apparatus. In an embodiment the fluidhandling system may supply immersion fluid and therefore be a fluidsupply system. In an embodiment the fluid handling system may at leastpartly confine immersion fluid and thereby be a fluid confinementsystem. In an embodiment the fluid handling system may form a barrier toimmersion fluid and thereby be a barrier member, such as a fluidconfinement structure. In an embodiment the fluid handling system maycreate or use a flow of gas, for example to help in controlling the flowand/or the position of the immersion fluid. The flow of gas may form aseal to confine the immersion fluid so the fluid handling structure maybe referred to as a seal member; such a seal member may be a fluidconfinement structure. In an embodiment, immersion liquid is used as theimmersion fluid. In that case the fluid handling system may be a liquidhandling system. In reference to the aforementioned description,reference in this paragraph to a feature defined with respect to fluidmay be understood to include a feature defined with respect to liquid.

One of the arrangements proposed is for a liquid supply system toprovide liquid on only a localized area of the substrate and in betweenthe final element of the projection system and the substrate using aliquid confinement system (the substrate generally has a larger surfacearea than the final element of the projection system). One way which hasbeen proposed to arrange for this is disclosed in PCT patent applicationpublication no. WO 99/49504. As illustrated in FIGS. 2 and 3, liquid issupplied by at least one inlet IN onto the substrate W as indicated byarrows, preferably along the direction of movement of the substrate Wrelative to the final element, and is removed by at least one outlet OUTafter having passed under the projection system PS as indicated byarrows. That is, as the substrate W is scanned beneath the element in a−X direction, liquid is supplied at the +X side of the element and takenup at the −X side. FIG. 2 shows the arrangement schematically in, whichliquid is supplied via inlet IN and is taken up on the other side of theelement by outlet OUT which is connected to a low pressure source. Inthe illustration of FIG. 2 the liquid is supplied along the direction ofmovement of the substrate W relative to the final element, though thisdoes not need to be the case. Various orientations and numbers of in-and out-lets positioned around the final element are possible, oneexample is illustrated in FIG. 3 in which four sets of an inlet IN withan outlet OUT on either side are provided in a regular pattern aroundthe final element.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets. INon either side of the projection system PS as indicated by arrows and isremoved by a plurality of discrete outlets OUT arranged radiallyoutwardly of the inlets IN as indicated by arrows. The inlets IN and OUTcan be arranged in a plate with a hole in its center and through whichthe projection beam is projected. Liquid is supplied by one groove inletIN on one side of the projection system PS and removed by a plurality ofdiscrete outlets OUT on the other side of the projection system PS,causing a flow of a thin film of liquid between the projection system PSand the substrate. W. The choice of which combination of inlet IN andoutlets OUT to use can depend on the direction of movement of thesubstrate W (the other combination of inlet IN and outlets OUT beinginactive).

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, the idea of atwin or dual stage immersion lithography apparatus is disclosed. Such anapparatus has two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table. PCT patent application publication WO2005/064405 discloses an all wet arrangement in which the immersionliquid is unconfined. In such a system the whole top surface of thesubstrate is covered in liquid. This may be advantageous because thenthe whole top surface of the substrate is exposed to the substantiallysame conditions. This has an advantage for temperature control andprocessing of the substrate. In WO 2005/064405, a liquid supply systemprovides liquid to the gap between the final element of the projectionsystem and the substrate. That liquid is allowed to leak over theremainder of the substrate. A barrier at the edge of a substrate tableprevents the liquid from escaping so that it can be removed from the topsurface of the substrate table in a controlled way. Although such asystem improves temperature control and processing of the substrate,evaporation of the immersion liquid may still occur. One way of helpingto alleviate that problem is described in United States patentapplication publication no. US 2006/0119809. A member is provided whichcovers the substrate in all positions and which is arranged to haveimmersion liquid extending between it and the top surface of thesubstrate and/or substrate table which holds the substrate.

A fluid handling system in an immersion lithographic apparatus maycomprise a two-phase extraction system. The extraction system may beconfigured to remove immersion liquid from a position to which it hasbeen supplied. Typically, such an extraction system extracts a mixtureof gas and liquid. For example, the gas could be gas from thesurrounding atmosphere or a contactless seal (e.g. gas knife) such asthat illustrated in FIG. 5. The liquid could be immersion liquid.

SUMMARY

The two-phase extracted flow of a two-phase extraction system may beanisotropic and may have unstable flow characteristics. This can lead toundesirable mechanical effects, such as unwanted vibrations on thesubstrate and/or substrate table. Imaging errors may result.

It is desirable, for example, to provide a fluid handling system inwhich vibrations (which may observed as an imaging error) generated bytwo-phase extraction are reduced or eliminated.

According to an embodiment of the invention, there is provided a fluidextraction system to extract a two-phase fluid in a lithographicapparatus. The fluid extraction system comprises an extraction channelfor two-phase fluid flow therethrough. The fluid extraction system alsocomprises a buffer chamber containing a volume of gas, the bufferchamber fluidly connected to the extraction channel. The fluidextraction system is configured such that liquid is substantiallyprevented from entering the buffer chamber.

According to an embodiment of the invention, there is provided a methodof reducing a pressure fluctuation of an immersion liquid used in animmersion lithographic apparatus. The method comprises extracting atwo-phase fluid from a location in the immersion lithographic apparatususing a fluid extraction system. The method also comprises reducing apressure fluctuation in the two-phase fluid being extracted by using abuffer chamber of the fluid extraction system.

According to an embodiment of the invention, there is provided a fluidextraction system to extract a two-phase fluid in a lithographicapparatus. The fluid extraction system comprises an extraction channelfor two-phase fluid flow therethrough. The fluid extraction system alsocomprises a separation tank fluidly connected to the extraction channel,and configured to receive the two-phase fluid flow from the extractionchannel. At least a portion of a wall of the extraction channel and/orat least a portion of a wall of the separation tank comprises a flexibleboundary portion configured to deform in response to a change in thepressure differential across it so as to reduce a fluctuation inpressure of the two-phase fluid in the fluid extraction system.

According to an embodiment of the invention, there is provided a methodof reducing a pressure fluctuation of an immersion liquid used in animmersion lithographic apparatus. The method comprises extracting atwo-phase fluid from a location in the immersion lithographic apparatususing a fluid extraction system. The method also comprises reducing apressure fluctuation in the two-phase fluid by using a flexible boundaryportion of the fluid extraction system, the flexible boundary portionconfigured to change shape in response to a change in pressuredifferential across the flexible boundary portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 is a schematic illustration of a fluid handling system comprisinga fluid extraction system according to an embodiment of the invention;

FIG. 7 is a schematic illustration of a buffer chamber for use with afluid handling system comprising a fluid extraction system according toan embodiment of the invention;

FIG. 8 is a schematic illustration of a fluid handling system comprisinga fluid extraction system according to an embodiment of the invention;

FIG. 9 is a schematic illustration of a fluid handling system comprisinga fluid extraction system according to an embodiment of the invention;and

FIG. 10 is a schematic illustration of a fluid handling systemcomprising a fluid extraction system according to an embodiment of theinvention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device. MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT holds the patterning device. It holds thepatterning device in a manner that depends on the orientation of thepatterning device, the design of the lithographic apparatus, and otherconditions, such as for example whether or not the patterning device isheld in a vacuum environment. The support structure MT can usemechanical, vacuum, electrostatic or other clamping techniques to holdthe patterning device. The support structure MT may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure MT may ensure that the patterning device is at adesired position, for example with respect to the projection system. Anyuse of the terms “reticle” or “mask” herein may be considered synonymouswith the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more patterning device tables). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AM for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as a-outer anda-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device. MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table. WT is then shifted in theX and/or Y direction so that a different target portion C can beexposed. In step mode, the maximum size of the exposure field limits thesize of the target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable minor array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may be employed.

Arrangements for providing liquid between a final element of theprojection system and the substrate can be classed into at least twogeneral categories. These are the bath type (or submersed) arrangementand the so called localized immersion system. In the submersedarrangement, substantially the whole of the substrate and optionallypart of the substrate table is submersed in a liquid, such as in a bathor under a film of liquid. The localized immersion system uses a liquidsupply system to provide liquid to only a localized area of thesubstrate. In the latter category, the space filled by liquid is smallerin plan than the top surface of the substrate. The volume of liquid inthe space that covers the substrate remains substantially stationaryrelative to the projection system while the substrate moves underneaththat space.

A further arrangement, to which an embodiment of the present inventionmay be directed, is the all wet solution in which the liquid isunconfined. In this arrangement, substantially the whole top surface ofthe substrate and all or part of the substrate table is covered inimmersion liquid. The depth of the liquid covering at least thesubstrate is small. The liquid may be a film, such as a thin film, ofliquid on the substrate. Any of the liquid supply devices of FIGS. 2-5may be used in such a system. However, sealing features are not presentin the liquid supply device, are not activated, are not as efficient asnormal or are otherwise ineffective to seal liquid to only the localizedarea. Four different types of localized liquid supply systems areillustrated in FIGS. 2-5. The liquid supply systems disclosed in FIGS.2-4 are described above.

FIG. 5 schematically depicts a localized liquid supply system or fluidhandling structure with a barrier member or fluid confinement structure12, which extends along at least a part of a boundary of the space 11between the final element of the projection system PS and the substratetable WT or substrate W. (Please note that reference in the followingtext to surface of the substrate W refers in addition or in thealternative to a surface of the substrate table WT, unless expresslystated otherwise.) The fluid confinement structure 12 is substantiallystationary relative to the projection system PS in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). In an embodiment, a seal is formed between thefluid confinement structure 12 and the surface of the substrate W andmay be a contactless seal such as a gas seal or fluid seal.

The fluid confinement structure 12 at least partly contains liquid inthe space 11 between a final element of the projection system PS and thesubstrate W. A contactless seal, such as a gas seal 16, to the substrateW may be formed around the image field of the projection system PS sothat liquid is confined within the space 11 between the substrate Wsurface and the final element of the projection system PS. The space 11,is at least partly formed by the fluid confinement structure 12positioned below and surrounding the final element of the projectionsystem PS. Liquid is brought into the space 11 below the projectionsystem PS and within the fluid confinement structure 12 by liquid inlet13. The liquid may be removed by liquid outlet 13. The fluid confinementstructure 12 may extend a little above the final element of theprojection system PS. The liquid level rises above the final element sothat a buffer of liquid is provided. In an embodiment, the fluidconfinement structure 12 has an inner periphery that at the upper endclosely conforms to the shape of the projection system PS or the finalelement thereof and may, e.g., be round. At the bottom, the innerperiphery closely conforms to the shape of the image field, e.g.,rectangular, though this need not be the case.

The liquid is contained in the space 11 by the gas seal 16 which, duringuse, is formed between the bottom of the fluid confinement structure. 12and the surface of the substrate W. The gas seal 16 is formed by gas,e.g. air or synthetic air but, in an embodiment, N₂ or another inertgas. The gas in the gas seal 16 is provided under pressure via inlet 15to the gap between fluid confinement structure 12 and substrate W. Thegas is extracted via outlet 14. The overpressure on the gas inlet 15,vacuum level on the outlet 14 and geometry of the gap are arranged sothat there is a high-velocity gas flow 16 inwardly that confines theliquid. The force of the gas on the liquid between the fluid confinementstructure 12 and the substrate W contains the liquid in a space 11. Eachopening (i.e. inlet or outlet) may be an annular groove which surroundsthe space 11. The annular groove may be continuous or discontinuous. Theflow of gas 16 is effective to contain the liquid in the space 11. Sucha system is disclosed in United States patent application publicationno. US 2004-0207824.

An embodiment of the invention may be applied to a fluid handlingstructure used in an immersion apparatus. The example of FIG. 5 is a socalled localized area arrangement in which liquid is only provided to alocalized portion of the top surface of the substrate W at any one time.Other arrangements are possible, including fluid handling systems whichmake use of a single phase extractor (whether or not it works in twophase mode) as disclosed, for example, in United States patentapplication publication no US 2006-0038968. In this regard, it will benoted that a single phase extractor can work in two phase mode. In anembodiment, a single phase extractor may comprise an inlet which iscovered in a porous material which is used to separate liquid from gasto enable single-liquid phase liquid extraction. A chamber downstream ofthe porous material is maintained at a slight under pressure and isfilled with liquid. The under pressure in the chamber is such that themeniscuses formed in the holes of the porous material prevent ambientgas from being drawn into the chamber. However, when the porous surfacecomes into contact with liquid there is no meniscus to restrict flow andthe liquid can flow freely into the chamber. The porous material has alarge number of small holes, e.g. of diameter in the range of 5 to 50μm. In an embodiment, the porous material is at least slightlyliquidphilic (e.g., hydrophilic), i.e. having a contact angle of lessthan 90° to the immersion liquid, e.g. water. In an embodiment, theliquid handling system may have an opening, such as an outlet, coveredwith a porous member.

Another arrangement which is possible is one which works on a gas dragprinciple. The so-called gas drag principle has been described, forexample, in United States patent application publication no. US2008-0212046 and U.S. patent application no. US 61/071,621 filed on 8May 2008. In that system the extraction openings (e.g., holes) arearranged in a shape which desirably has a corner. The corner may bealigned with the stepping and scanning directions. This reduces theforce on the meniscus between two openings in the surface of the fluidhanding structure for a given relative velocity between the substratetable WT (including the substrate W) and the fluid confinement structurein the step or scan direction compared to if the two outlets werealigned perpendicular to the direction of scan. Desirably the relativevelocity may be a velocity range. The openings of a fluid handlingstructure may have extraction openings which have no covering or have acovering made of a porous material.

An embodiment of the invention can be applied to any system in which atwo-phase fluid flow may be extracted. For example, an embodiment of theinvention could be applied to a fluid handling structure used in an allwet immersion apparatus. In the all wet embodiment, fluid is allowed tocover substantially the whole of the top surface of the substrate table,for example, by allowing liquid to leak out of a confinement structurewhich confines liquid to between the final element of projection systemand the substrate. An example of a fluid handling structure for an allwet embodiment can be found in U.S. patent application no. U.S.61/136,380 filed on 2 Sep. 2008.

FIG. 6 illustrates schematically, in cross-section, a fluid handlingsystem 100 according to an embodiment of the invention. The fluidhandling system 100 at least partly confines an immersion liquid to animmersion space 11 between the projection system PS and the substrate W.The fluid handling system 100 can provide liquid to the immersion space11. However, for simplicity, any openings (i.e. inlets and/or outlets)for allowing the immersion liquid to enter and/or exit the immersionspace 11 are not illustrated. The openings may be of any suitable typeand configuration for example those described with reference to FIG. 5.

The fluid handling system may be used to supply, confine and/or controla liquid, for example an immersion liquid. However, it will beappreciated that in some examples, a gas may be used in the fluidhandling system, for example in a sealing element. Thus, in theembodiments of the invention described herein, the term fluid handlingsystem will be used. However, in some embodiments, the term fluidhandling system could be replaced with liquid handling system. In such aliquid handling system gas is not supplied. However, in an embodimentthe liquid handling system has an extraction opening which extracts gasand liquid in two phase fluid flow.

As can be seen from FIG. 6, the fluid handling system 100 comprises agas seal 16 arranged to confine the immersion liquid (shown in FIGS. 5,6, 8, 9 and 10 as a vertical hatched area) to the immersion space 11. Atthe boundary between the immersion liquid and the gas, the immersionliquid may have a meniscus 17. The gas seal 16 may be substantially thesame as the gas seal 16 described above in relation to FIG. 5. As such,it may have an opening 15 for use as a gas inlet 15. (which may be at anoverpressure), and an opening 14 for use as a gas outlet 14 (which maybe at an underpressure). In the following description, the opening 15will be referred to as gas inlet 15 (or inlet 15), and the opening 14will be referred to as gas outlet 14 (or outlet 14). Any other suitablegas seal may be used.

In an embodiment, a mixture of sealing gas from the gas seal 16 andimmersion liquid from the immersion space 11 is extracted through theoutlet 14 of the gas seal 16. Thus, a two-phase fluid flow of liquid andgas is extracted through the outlet 14.

Having been extracted through the outlet 14, the two-phase fluid flowsinto and through an extraction channel 40 which is connected to theoutlet 14. The extraction channel 40 may comprise an extraction chamber30 into which the extracted two-phase fluid flow can enter. Theextraction chamber 30 may be located inside the confinement structure12. The extraction channel 40 may comprise an extraction duct, orpassageway, 35. The extraction channel 40 may be at least partiallylocated inside the confinement structure 12. The extraction channel 40may be at least partially located outside the fluid confinementstructure 12.

The extracted two-phase fluid flow flows along the extraction channel 40due to an underpressure being applied to the exit of the extractionchannel 40. At the exit of the extraction channel 40, the two-phasefluid is supplied into a settling chamber 50, such as a separation tank.As such, the settling chamber 50 is configured to receive the extractedtwo-phase fluid from the extraction channel 40. Inside the settlingchamber 50, the two-phase fluid mixture separates. Thus, the liquid 58settles to the bottom of the settling chamber 50, and may be extractedthrough an opening, e.g. exit 54 (for example by using a liquidextraction pump). The gas 56 may then be removed from the settlingchamber 50 through a different exit 52. The different exit 52 may, forexample, be an opening at the top of the settling chamber 50, or anopening defined in the settling chamber 50 at least at a higher positionthan the liquid exit 54. A pump (not illustrated) may be attached to thegas exit 52. This pump may be used to generate a regulated underpressure(or regulated vacuum) in the settling chamber 50. This underpressuregenerated by the pump may act throughout the extraction system. So thepump may generate an underpressure in the settling chamber 50, along theextraction channel 40 (including optionally in the extraction passageway35 and extraction chamber 30) and at the gas seal outlet 14. The pumpthat may be attached to the gas exit 52 of the settling chamber 50 maybe used to generate the underpressure for extracting the flow throughgas seal outlet 14.

The pump used to generate the underpressure for the gas exit 14 of thegas seal 16 may be located at any suitable position, for example at anypoint along the extraction channel 40. For example, alternatively oradditionally it may not be necessary to have a settling chamber 50. Thepump would be located at a position other than at the exit to a settlingchamber 50. For example, the pump could be located at an opening in theextraction channel or adjacent to the gas seal outlet 14. Please notethat reference in this paragraph to the location of the pump includesreference to a connection to the pump.

In a conventional fluid extraction system, a two-phase fluid flow (forexample, of sealing gas used for the gas seal 16 and the immersionliquid in the immersion space 11) is extracted through gas seal outlet14 and along the extraction channel 40. Because the flow is two-phase,the pressure acting in the fluid extraction system (i.e. including atthe gas seal outlet 14) can vary. This may be because the two phasefluid flow is unstable. Some two phase fluid flow types may be stableand exhibit smooth flow. In such two phase fluid flow regimes theproportion of liquid in the fluid flow may be small, or the two phasesflow separately, e.g. co-axially. Vibrations tend not to be caused bysuch smooth flow regimes. However, in an unstable two phase fluid flowregime, such as slug flow, the liquid may occasionally (such as in anoscillating, repetitive manner) or continuously block the conduitthrough which the two phase fluid flows. Such behavior causes a pressurefluctuation in the two phase fluid flow. For example, the pressureacting due to the pump attached to the gas exit 52 in the fluidextraction system can vary with the proportion of gas to liquid that iscurrently being extracted through gas seal outlet 14, and/or theproportion of gas to liquid that is currently in the extraction channel40.

The pressure fluctuation, for example, in the two phase fluid flow canbe transmitted (for example, via the gas seal outlet 14) to theimmersion liquid and/or the gas between the gas seal outlet 14 and thesubstrate W and/or substrate table WT. These pressure fluctuations canthus result in forces being transmitted through the immersion liquidconfined in the immersion space 11 and/or through the gas to thesubstrate W or the substrate table WT. Thus, unwanted motion and/oracceleration of the substrate W and/or the substrate table WT canresult. Such unwanted movement could be in, for example, the z axis (theoptical axis of the projection system PS), or the x and/or y axes (inthe plane of the substrate surface). This motion may be transferred tothe substrate table WT by the fluid between the confinement structure 12and the substrate table WT. Unwanted motion and/or acceleration of thesubstrate W, substrate table WT, or both, relative to the projectionsystem PS can lead to inaccuracies (for example focus and overlayerrors) in the exposure.

The aforementioned paragraph refers to application of the forcesdirectly from the two phase fluid flow through intermediate fluid.However, the pressure fluctuations may be transmitted to the substrate Wand/or substrate table WT by another path, by interaction between theconfinement structure 12 and the substrate table WT. This interactionmay be determined by the relative stiffness and damping properties ofthe substrate table WT and the confinement structure 12. For example, apressure fluctuation may cause motion of the confinement structure 12,or one or more of its components. Such motion may be relative to thesubstrate table WT. The forces causing the motion, or at least some ofthe forces, may be transferred to the substrate table WT by the fluidbetween the confinement structure 12 and the substrate table WT (i.e.the immersion liquid as a liquid is incompressible), and cause unwantedmotion and/or acceleration of the substrate W and/or substrate table WT.

In order to reduce the pressure fluctuation in the two-phase fluid flowthat is extracted from gas seal outlet 14, a buffer chamber 20 isprovided as shown in FIG. 6. The buffer chamber 20 defines a buffervolume. As shown in FIG. 6, the buffer chamber 20 is attached to theextraction chamber 30 via a connection pipe 25 or conduit. The buffervolume is thus fluidly in communication with the extracted two-phasefluid (i.e. two-phase extraction system). In an embodiment, the bufferchamber 20 may be fluidly attached to another part of the fluidextraction system via a suitable connection conduit. For example, thebuffer chamber 20 could be attached to another part of the extractionchannel 40, such as the extraction passageway 35. As shown in FIG. 6,the buffer chamber 20 may be located separately from other components ofthe apparatus. However, it may be possible, to incorporate the bufferchamber 20 into one or more other parts of the lithographic apparatus.For example, it may be possible to incorporate (or locate) the bufferchamber 20 into the confinement structure 12, or into the projectionsystem PS. The buffer chamber 20 may be provided as part of theextraction chamber 30.

The buffer chamber 20 (which may be referred to as an expansion vessel20) can reduce the pressure fluctuation in the two-phase extractionsystem. For example the volume of gas contained in the buffer chamber 20may help to absorb a fluctuation present in the extraction system. Thefluctuation may be created in and/or transmitted through the extractionsystem. Such a fluctuation which is absorbed in the buffer chamber 20may include a pressure fluctuation that would otherwise be present inthe extraction channel 40, extraction chamber 30, the extractionpassageway 35, and/or at the gas seal outlet 14. It is desirable for thebuffer chamber 20 to be sufficiently large to absorb such a pressurefluctuation, desirably substantially completely. In an embodiment thevolume of gas in the buffer chamber 20 would be between from two timesto five times as large as the total volume of the rest of the fluidextraction system (i.e. the whole of the extraction channel 40 (whichmay comprise the extraction chamber 30) but not including the settlingchamber 50). Desirably, the volume of gas in the buffer chamber 20 wouldbe in the range of from three times to four times as large as the totalvolume of the rest of the fluid extraction system. The buffer chamber 20may be four times as large as the total volume of the rest of the fluidextraction system. The shape of the buffer chamber 20 may not beimportant. Thus, the shape of the buffer chamber 20 could be any shape,for example, be a cube, a cuboid, a rhomboid, or a sphere.

As explained above, the buffer chamber 20 is arranged to be connected tothe two-phase fluid flow via a connection pipe 25. However, the bufferchamber 20 is arranged to be separate from the main extraction flow pathfor the gas and/or the liquid in the two phase fluid flow. That is, thebuffer chamber 20 is arranged so as not to be part of the mainextraction flow path. As such, the volume of gas in the buffer chamber20 is substantially static i.e. the flow rate in the buffer chamber 20is substantially zero. At least 70%, desirably 90%, more desirablysubstantially all of the fluid (including the gas) in the two phasefluid flow passes through the extraction channel, for example,downstream of the buffer chamber. Thus, substantially no gas isextracted from the extraction system through the buffer chamber.

In an embodiment, the buffer chamber 20 is a dry volume. As such, thebuffer chamber 20 may contain fluid in a single phase, i.e. gas.Desirably, the buffer chamber contains no liquid. Containing gas but noliquid can help the buffer chamber 20 to absorb a pressure fluctuationmore effectively. The extraction system may be arranged such thatsubstantially no liquid (for example from the two phase fluid flow) canenter the buffer chamber 20. In order to help ensure that substantiallyno liquid enters the buffer chamber 20, a purge flow 24 may be applied.This purge flow 24 may be an inflow of gas which acts to prevent liquidentering the buffer chamber 20 through the connecting pipe 25 whichconnects the buffer chamber 20 to the fluid extraction system. The purgeflow 24 is optional, and may not be required in some embodiments.

In FIG. 6, the buffer chamber 20 is shown as being an enclosed volumewith rigid walls. However, some embodiments may comprise modificationsof this arrangement. For example, in some embodiments there may be anopening in at least one of the walls of the buffer chamber 20 that isopen to the atmosphere. The opening would be relatively small. Forexample, the opening could be between from 0.1 mm² and 10 mm².Desirably, the opening could be between from 0.5 mm² and 5 mm².Desirably, the opening could be approximately 1 mm². Such an opening tothe atmosphere could additionally or alternatively be provided to aboundary of the extraction channel 40, for example in the extractionpassageway 35 and/or the extraction chamber 30.

Alternatively or additionally, at least one of the walls of the bufferchamber 20 may be flexible. For example, wall 22 as shown in FIG. 6 maybe constructed from a flexible material (for example, a suitablepolymer) that can elastically deform as a result of a pressure changeacross it. The wall may comprise a flexible component, which may beresilient. In FIG. 6, this flexible wall (or flexible boundary portion)is shown as dashed line 22A. The flexible wall can further help toreduce a pressure fluctuation in the fluid extraction system.

FIG. 7 shows, in cross-section, a modified buffer chamber 20. Thisbuffer chamber 20 includes a flap 60 attached to a wall 22 of the bufferchamber 20. The flap 60 may operate as a valve and it may be in the formof a plate or sheet. When closed, the flap 60 seals the buffer chamber20 so as to form an enclosed volume. When open, the flap 60 allows apath fluidly to connect the environment to the buffer chamber 20. Whenthe pressure in the buffer chamber 20 reduces below a certain level (forexample due to a pressure fluctuation in the fluid extraction system),the flap 60 may open. This opening of the valve, i.e. flap 60, may allowhigher pressure gas (e.g. environmental air) to enter the buffer chamber20. This can help to increase the pressure in the buffer chamber 20,thereby further reducing the pressure fluctuation 32 in the fluidextraction system.

In order to bias the flap 60 to the closed position, a biasing member 62may be provided. For example, the biasing member 62 may be resilient,and may be a spring. The pressure difference either side of the flap 60to overcome the biasing member 62 may be adjusted by an adjusting member64. For example, the adjusting member 64 may be a screw. The screw maybe configured to adjust the compression of the biasing member 62 (or thecompressive force provided by the biasing member 62).

Although the flap 60 is shown in FIG. 7 as being applied to the bufferchamber 20, it will be understood that such a flap 60 could beincorporated into the fluid extraction system at any suitable location.For example, a flap 60 could be provided on the fluid extraction channel40 (for example, the extraction chamber 30 and/or the extractionpassageway 35) directly.

FIG. 8 shows an embodiment of the invention in which the buffer chamber20 comprises a buffer channel (or pipe) 21. The buffer channel 21 runssubstantially parallel to the extraction channel 40 (in particularsubstantially parallel to the extraction passageway 35). As shown inFIG. 8, the buffer channel 21 may be connected to the extraction channel40 via at least one interconnection 23. The buffer pipe 21 is shown inFIG. 8 as being partially inside the confinement structure 12 andpartially outside the confinement structure 12. In an embodiment, thebuffer channel 21 could be located entirely within the fluid confinementstructure 12. The buffer channel 21 could be located entirely outsidethe fluid confinement structure 12.

The purpose of the buffer channel 21 is substantially the same as thepurpose of the buffer chamber 20 of the FIG. 6 embodiment. The bufferchannel 21 acts to reduce the pressure fluctuation in the fluidextraction system. The buffer channel 21 helps to reduce thedisturbances experienced by the substrate W and/or substrate table WT.The buffer channel 21 provides an elastic volume of gas which may act toreduce pressure fluctuation in the fluid handling system 200.

Any of the arrangements and/or modifications to the buffer chamber 20 ofan embodiment as shown in FIG. 6 may be applied to the buffer channel 21of the embodiment of the fluid handling system 200 shown in FIG. 8. Anyone or more of the following features (provided in a non-limiting list)may be applied to the buffer channel 21: a purge flow 24, a flexiblewall, a flap 60, and/or an opening to the atmosphere.

FIG. 9 shows a fluid handling system 300 according to an embodiment ofthe invention. In FIG. 9 is shown the extraction of a two-phase fluidthrough an exit (or opening) 14 of the gas seal 16 as shown in FIGS. 6and 8. In FIG. 9, the two-phase fluid flows along the extraction channel40 (which may or may not include an extraction chamber 30 and/or anextraction passageway 35) and into a separation chamber 50. As describedabove in relation to other embodiments, the two-phase fluid separatesinto its two constituent phases in the settling chamber 50, namely agaseous phase 56 and a liquid phase 58. The liquid phase 58 may beextracted from the fluid settling chamber 50 via an opening (i.e. afluid outlet) 54. The separated gas may be extracted from the fluidsettling chamber 50 via a different opening (i.e. a gas exit) 52.

In the embodiment shown in FIG. 9, at least a part of the boundary ofthe settling chamber 50 is flexible. For example, at least one wall, orat least a part of at least one wall, of the settling chamber 50 may bemade from a flexible material, so as to form a flexible boundary portion70. The flexible boundary portion may be resilient. Desirably, theflexible boundary portion 70 can elastically deform. For example, theflexible boundary portion 70 may elastically deform due to a change in apressure differential applied across it. The flexible boundary portion70 may be, for example, a flexible membrane. The boundary portion 70 maybe made from a suitable material, for example a material which canelastically deform, for example an appropriate polymer material.

In operation, as the pressure in the fluid extraction system varies (forthe reasons explained above), the shape of the flexible boundary portion70 may change due to a change in pressure difference across it. In thisway, the shape and size of the separation chamber 50 can change inresponse to the pressure inside the settling chamber 50. Any pressurefluctuation in the fluid extraction system (including the extractionchannel 40 and at the gas seal outlet 14) can be reduced, and desirablyeliminated.

In FIG. 9, the flexible boundary portion 70 is shown as being providedto the settling chamber 50. Additionally or alternatively, a flexibleboundary portion 70 may be present on any other portion of the fluidextraction system, for example as part of any component of the fluidextraction system. For example, a flexible boundary portion 70 may beprovided to at least a portion of the extraction channel 40, for examplethe extraction passageway 35 and/or the extraction chamber 30.

In an embodiment, as shown in FIG. 9, there is no buffer chamber 20 orbuffer channel 21. However, in an embodiment a buffer chamber 20 and/ora buffer channel 21 may be present in addition to the features presentin the apparatus shown in FIG. 9.

As such, the features shown and described with reference to any of theFIGS. 6, 7, 8 and/or 9 (including optional features relating thereto)alone or in combination, may be combined. Thus, an apparatus having aflexible boundary portion 70 as shown in FIG. 9 may include a bufferchamber 20 (as described above in relation to FIG. 6), and/or a bufferchannel 21 (as described above in relation to FIG. 8). Furthermore, asmentioned above, a flexible boundary portion may additionally oralternatively be provided to the buffer chamber 20 and/or the bufferchannel 21.

In FIG. 9, the side of the flexible boundary portion 70 that faces awayfrom the separation chamber 50 may be open to atmospheric pressure.However, in an embodiment of a fluid handling system 400, as shown inFIG. 10, the side of the flexible boundary portion 70 that faces awayfrom the settling chamber 50 may form part of the boundary of asecondary chamber 80, or a pressure control chamber 80.

The pressure control chamber 80 is provided adjacent the separationchamber 50. The pressure control chamber 80 has at least a part of itsboundary formed by the flexible boundary portion 70 that forms at leasta part of the boundary of the separation chamber 50. A side of theflexible boundary portion 70 is exposed to the pressure in theseparation chamber 50 (which is related to the pressure in theextraction channel 40 and at the gas seal outlet 14, as describedabove). The other side of the flexible boundary portion is exposed tothe pressure in the pressure control chamber 80.

The pressure in the pressure control chamber 80 can be regulated to bedifferent from atmospheric pressure, for example to be lower thanatmospheric pressure. This can be achieved in the following way. Thepressure control chamber may have an opening 84 for inlet of gas, and anopening 82 for outlet of gas. The pressure in the pressure controlchamber 80 can be reduced below atmospheric pressure, for example, byusing an extraction pump at the exit 82 of the pressure control chamber80. Lowering the pressure inside the pressure control chamber 80 causesthe pressure differential across the flexible boundary portion 70 toreduce in comparison to the arrangement in which the pressure controlchamber 80 is absent as shown in FIG. 9. That is, in comparison to thearrangement in which the outside face of the flexible boundary portion70 is exposed to atmospheric pressure. The pressure inside the pressurecontrol chamber 80 could be set to be approximately the same as thepressure inside the separation chamber 50. Reducing the pressuredifferential across the flexible boundary portion 70 is desirablebecause it can improve the response of the flexible boundary portion 70to a change in pressure inside the settling chamber 50 (i.e. to a changein pressure of the two-phase fluid being extracted). For example,providing the pressure control chamber 80 can mean that the flexibleboundary portion 70 is responsive to a smaller change in pressure in thesettling chamber 50 and/or responds more quickly to a given pressurechange in the settling chamber 50.

As described above, the flexible boundary portion 70 may be provided toany suitable part of the fluid extraction system, for example on theextraction channel 40 and/or on the buffer chamber 20 and/or the bufferchannel 21. A pressure control chamber 80 as described above in relationto FIG. 10 may be provided to any part of the extraction system that hasa flexible boundary portion 70. As such, the pressure on the side of theflexible boundary portion 70 that is not exposed to a part of the fluidextraction system can be controlled using a pressure control chamber 80(which may be referred to as a pressure control tank), wherever theflexible boundary portion 70 is located.

Embodiments of the invention have been described herein with referenceto two-phase extraction from a gas seal. However, an embodiment of theinvention may be applied to any apparatus involving a two-phase fluidextraction of gas and liquid. In particular, an embodiment of theinvention may be applied to any part of a lithographic apparatus (forexample an immersion lithographic apparatus) in which two-phase fluidextraction is performed. As described above, an embodiment of theinvention may help to reduce, or eliminate, a pressure fluctuation in atwo-phase extraction system. For example, an embodiment of the inventionmay be applied to any gas seal for preventing immersion liquid fromaccessing the underside of a substrate when positioned on a substratetable (which may be known as a wafer edge seal, or WES). Additionally oralternatively, an embodiment of the invention may be applied to atwo-phase extraction system used to extract fluid from between asubstrate and a substrate table (which may be known as a bubbleextraction system, or BES). Additionally or alternatively, an embodimentof the invention may be applied to a two-phase extraction system used toextract fluid from a system used during substrate swap, when changingthe table underneath the projection system PS and the fluid handlingstructure 12. In such an arrangement, the two phase extraction systemwould extract liquid in a two phase fluid flow from a gap between asubstrate table and a shutter member.

At substrate swap, an exposed substrate is removed from the substratetable. WT and a new substrate for exposure is placed in the substratetable. During substrate swap, the shutter member is placed underneaththe projection system and the fluid confinement structure 12 so as tokeep immersion liquid in the space 11. The shutter member may be: aclosing member, such as a closing disc, which is co-planar with thesubstrate table WT, present in a recess in the substrate table WT andwhich may be transferred to the new table; another substrate table WT; ameasurement table which is configured not to support a substrate; or aswap bridge which acts as a bridge between two tables. Between thesurface of the substrate table and the shutter member may be a gap intowhich liquid may escape from the fluid confinement structure, forexample as the gap passes underneath the fluid confinement structure.

As will be appreciated, any of the above described features can be usedwith any other feature and it is not only those combinations explicitlydescribed which are covered in this application.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to, a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm). The term“lens”, where the context allows, may refer to any one or combination ofvarious types of optical components, including refractive and reflectiveoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the embodiments of the invention maytake the form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein. Further, themachine readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent memories and/or data storage media.

The controllers described herein may each or in combination be operablewhen the one or more computer programs are read by one or more computerprocessors located within at least one component of the lithographicapparatus. The controllers may each or in combination have any suitableconfiguration for receiving, processing, and sending signals. One ormore processors are configured to communicate with the at least one ofthe controllers. For example, each controller may include one or moreprocessors for executing the computer programs that includemachine-readable instructions for the methods described above. Thecontrollers may include data storage medium for storing such computerprograms, and/or hardware to receive such medium. So the controller(s)may operate according the machine readable instructions of one or morecomputer programs.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath, only on a localized surface area of the substrate, or isunconfined. In an unconfined arrangement, the immersion liquid may flowover the surface of the substrate and/or substrate table so thatsubstantially the entire uncovered surface of the substrate table and/orsubstrate is wetted. In such an unconfined immersion system, the liquidsupply system may not confine the immersion fluid or it may provide aproportion of immersion liquid confinement, but not substantiallycomplete confinement of the immersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more fluid openingsincluding one or more liquid openings, one or more gas openings or oneor more openings for two phase fluid flow. The openings may each be aninlet into the immersion space (or an outlet from a fluid handlingstructure) or an outlet out of the immersion space (or an inlet into thefluid handling structure). In an embodiment, a surface of the space maybe a portion of the substrate and/or substrate table, or a surface ofthe space may completely cover a surface of the substrate and/orsubstrate table, or the space may envelop the substrate and/or substratetable. The liquid supply system may optionally further include one ormore elements to control the position, quantity, quality, shape, flowrate or any other features of the liquid.

In an embodiment there is provided a fluid extraction system to extracta two-phase fluid in a lithographic apparatus. The fluid extractionsystem comprises: an extraction channel, and a buffer chamber. Theextraction channel is for two-phase fluid flow therethrough. The bufferchamber contains a volume of gas. The buffer chamber is fluidlyconnected to the extraction channel. The fluid extraction system isconfigured such that liquid is substantially prevented from entering thebuffer chamber.

The fluid extraction system may be configured such that substantially nogas is extracted from the fluid extraction system through the bufferchamber. The fluid extraction system may be configured such that atleast 70%, desirably 90%, more desirably all of the gas extracted fromthe extraction system passes through the extraction channel downstreamof the buffer chamber. The extraction channel may define a pathway forthe flow of the two-phase fluid.

The extraction channel may comprise an extraction chamber through whichthe pathway passes. The extraction chamber may be located in a barriermember of the fluid extraction system. The buffer chamber may be fluidlyconnected to the extraction chamber via a connection conduit that isseparate from the extraction channel. The extraction channel maycomprise an extraction passageway. The extraction passageway may bedownstream of the extraction chamber. The extraction passageway may beconfigured to allow the two-phase fluid to flow there along. Theextraction channel may comprise an extraction passageway, downstream ofthe extraction chamber, along which, in use, the two-phase fluid flows.The buffer chamber may be fluidly connected to the extraction passagewayvia a connection conduit that is separate from the extraction channel.The buffer chamber may be fluidly connected to the extraction passagewayat a plurality of locations along the length of the extractionpassageway.

At least a part of the surface of the buffer chamber may be defined by aflexible membrane. The buffer chamber may have an opening that is influid communication with the atmosphere. The fluid extraction system maycomprise a purging device fluidly connected to the buffer chamber. Thepurging device may be configured to provide a gas into the bufferchamber. The fluid extraction system may comprise a separation tankfluidly connected to the extraction channel. The separation tank may beconfigured to receive two-phase fluid flow from the extraction channel.The buffer chamber may be fluidly connected to the extraction channel ata location between an opening of the extraction channel through whichthe two phase fluid enters the extraction system and the separationtank.

The volume of the buffer chamber may be at least four times that of theextraction channel. The fluid extraction system may comprise a pumpconfigured to reduce the pressure acting on the two-phase fluid flow soas to draw the two-phase fluid flow along the extraction channel. Thebuffer chamber may be configured to reduce a pressure fluctuation in thetwo-phase fluid.

The fluid extraction system may comprise a pressure regulator connectedbetween the atmosphere and the fluid extraction system, the pressureregulator configured to allow gas from the atmosphere to passtherethrough so as to bring the fluid extraction system into fluidcommunication with the atmosphere. The pressure regulator may beconnected between the atmosphere and the buffer chamber. The pressureregulator may be connected between the atmosphere and the extractionchannel.

The pressure regulator may comprise a biasing mechanism configured toprevent gas from passing through the pressure regulator if the pressuredifference either side of the pressure regulator is below a certainvalue.

In an embodiment there is provided a fluid handling system for animmersion lithographic apparatus comprising the fluid extraction systemdescribed herein.

In an embodiment there is provided an immersion lithographic apparatuscomprising the fluid extraction system as described herein. Theimmersion lithographic apparatus may comprise a projection system. Thefluid extraction system may be configured to remove fluid from a spacebetween the final element of the projection system and a substrateand/or substrate table.

In an embodiment there is provided an immersion lithographic apparatuscomprising: a support, a projection system and a fluid handling system.The support is constructed to support a patterning device that iscapable of imparting a radiation beam with a pattern in itscross-section to form a patterned radiation beam. The substrate table isconstructed to hold a substrate. The projection system is configured toproject the patterned radiation beam onto a target portion of thesubstrate. The fluid handling system, which may be as described herein,is configured to provide an immersion liquid between the projectionsystem and the substrate, or the substrate table, or both the substrateand the substrate table.

In an embodiment there is provided a method of reducing a pressurefluctuation of an immersion liquid in an immersion lithographicapparatus. The method comprises extracting and reducing. In theextracting, a two-phase fluid is extracted from a location in theimmersion lithographic apparatus using a fluid extraction system. In thereducing, a pressure fluctuation in the two-phase fluid being extractedis reduced by using a buffer chamber of the fluid extraction system.

The immersion lithographic apparatus may comprise a projection system.The location from which the two-phase fluid is extracted may be a spacebetween the final element of the projection system and a substrate, or asubstrate table, or both the substrate and the substrate table. Thefluid extraction system may extract a mixture of gas and immersionliquid.

In an embodiment there is provided a fluid extraction system to extracta two-phase fluid in a lithographic apparatus. The fluid extractionsystem comprises: an extraction channel, and a separation tank. Theextraction channel is for two-phase fluid flow therethrough. Theseparation tank is fluidly connected to the extraction channel. Thefluid separation tank is configured to receive the two-phase fluid flowfrom the extraction channel. At least a portion of a wall of theextraction channel and/or at least a portion of a wall of the separationtank comprises a flexible boundary portion configured to deform inresponse to a change in the pressure differential across it so as toreduce a fluctuation in pressure of the two-phase fluid in the fluidextraction system.

The flexible boundary portion may be a part of the boundary of theseparation tank. The fluid extraction system may comprise a pumpconnected to the separation tank so as to reduce the pressure inside theseparation tank to extract the two-phase fluid into the extractionchannel.

The fluid extraction system may comprise a pressure control chamber. Thepressure control chamber may have the flexible boundary portion as partof its boundary. The pressure control chamber may be configured toprovide a controlled pressure differential across the flexible boundaryportion. The pressure control chamber may be configured to provide asubstantially zero pressure difference across the flexible boundaryportion. The flexible boundary portion may form part of the separationtank. The pressure control chamber may be attached to the separationtank. The separation tank may be configured to separate the two-phasefluid flow into a liquid phase and a gas phase. The separation tank maybe configured to output the liquid phase and the gas phase throughdifferent outlets. The lithographic apparatus may be an immersionlithographic apparatus comprising a projection system. The fluidextraction system may be configured to remove fluid from a space betweenthe final element of the projection system and a substrate and/orsubstrate table.

In an embodiment there is provided a fluid handling system for animmersion lithographic apparatus comprising the fluid extraction systemas described herein.

In an embodiment there is provided an immersion lithographic apparatuscomprising: a support, a substrate table, a projection system, and afluid handling system. The support is constructed to support apatterning device that is capable of imparting a radiation beam with apattern in its cross-section to form a patterned radiation beam. Thesubstrate table is constructed to hold a substrate. The projectionsystem is configured to project the patterned radiation beam onto atarget portion of the substrate. The fluid handling system, which isdescribed herein, is configured to provide an immersion liquid betweenthe projection system and the substrate, or the substrate table, or boththe substrate and the substrate table.

In an embodiment there is provided a method of reducing a pressurefluctuation of an immersion liquid used in an immersion lithographicapparatus. The method comprises: extracting and reducing. In theextracting, a two-phase fluid is extracted from a location in theimmersion lithographic apparatus using a fluid extraction system. In thereducing, a pressure fluctuation in the two-phase fluid is reduced byusing a flexible boundary portion of the fluid extraction system. Theflexible boundary portion is configured to change shape in response to achange in pressure differential across the flexible boundary portion.

The immersion lithographic apparatus may comprise a projection system.The location from which the two-phase fluid is extracted may be a spacebetween the final element of the projection system and a substrate, or asubstrate table, or both the substrate and the substrate table. Thefluid extraction system may extract a mixture of gas and immersionliquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A fluid extraction system to extract a two-phase fluid in alithographic apparatus, the fluid extraction system comprising: anextraction channel for two-phase fluid flow therethrough; and a bufferchamber containing a volume of gas, the buffer chamber fluidly connectedto the extraction channel, wherein the fluid extraction system isconfigured such that liquid is substantially prevented from entering thebuffer chamber.
 2. The fluid extraction system of claim 1, configuredsuch that substantially no gas is extracted from the fluid extractionsystem through the buffer chamber.
 3. The fluid extraction system ofclaim 1, wherein the extraction channel defines a pathway for the flowof the two-phase fluid.
 4. The fluid extraction system of claim 3,wherein: the extraction channel comprises an extraction chamber throughwhich the pathway passes, the extraction chamber located in a barriermember of the fluid extraction system; and the buffer chamber is fluidlyconnected to the extraction chamber via a connection conduit that isseparate from the extraction channel.
 5. The fluid extraction system ofclaim 4, wherein: the extraction channel comprises an extractionpassageway, downstream of the extraction chamber, along which, in use,the two-phase fluid flows; and the buffer chamber is fluidly connectedto the extraction passageway via a connection conduit that is separatefrom the extraction channel.
 6. The fluid extraction system of claim 1,wherein at least a part of the surface of the buffer chamber is definedby a flexible membrane.
 7. The fluid extraction system of claim 1,wherein the buffer chamber has an opening that is in fluid communicationwith the atmosphere.
 8. The fluid extraction system of claim 1, furthercomprising a separation tank fluidly connected to the extraction channeland configured to receive two-phase fluid flow from the extractionchannel, wherein the buffer chamber is fluidly connected to theextraction channel at a location between an opening of the extractionchannel through which the two phase fluid enters the extraction systemand the separation tank.
 9. The fluid extraction system of claim 1,wherein the volume of the buffer chamber is at least four times that ofthe extraction channel.
 10. The fluid extraction system of claim 1,further comprising a pump configured to reduce the pressure acting onthe two-phase fluid flow so as to draw the two-phase fluid flow alongthe extraction channel.
 11. The fluid extraction system of claim 1,further comprising a pressure regulator connected between the atmosphereand the fluid extraction system, the pressure regulator configured toallow gas from the atmosphere to pass therethrough so as to bring thefluid extraction system into fluid communication with the atmosphere.12. A fluid handling system for an immersion lithographic apparatuscomprising the fluid extraction system of claim
 1. 13. An immersionlithographic apparatus comprising the fluid extraction system ofclaim
 1. 14. An immersion lithographic apparatus comprising: a supportconstructed to support a patterning device that is capable of impartinga radiation beam with a pattern in its cross-section to form a patternedradiation beam; a substrate table constructed to hold a substrate; aprojection system configured to projected the patterned radiation beamonto a target portion of the substrate; and a fluid handling systemaccording to claim 12 configured to provide an immersion liquid betweenthe projection system and the substrate, or the substrate table, or boththe substrate and the substrate table.
 15. A method of reducing apressure fluctuation of an immersion liquid in an immersion lithographicapparatus, the method comprising: extracting a two-phase fluid from alocation in the immersion lithographic apparatus using a fluidextraction system; and reducing a pressure fluctuation in the two-phasefluid being extracted by using a buffer chamber of the fluid extractionsystem.
 16. A fluid extraction system to extract a two-phase fluid in alithographic apparatus, the fluid extraction system comprising: anextraction channel for two-phase fluid flow therethrough; and aseparation tank fluidly connected to the extraction channel, andconfigured to receive the two-phase fluid flow from the extractionchannel, wherein at least a portion of a wall of the extraction channeland/or at least a portion of a wall of the separation tank comprises aflexible boundary portion configured to deform in response to a changein the pressure differential across it so as to reduce a fluctuation inpressure of the two-phase fluid in the fluid extraction system.
 17. Thefluid extraction system of claim 16, wherein the flexible boundaryportion is a part of the boundary of the separation tank.
 18. A fluidhandling system for an immersion lithographic apparatus comprising thefluid extraction system of claim
 16. 19. An immersion lithographicapparatus comprising: a support constructed to support a patterningdevice that is capable of imparting a radiation beam with a pattern inits cross-section to form a patterned radiation beam; a substrate tableconstructed to hold a substrate; a projection system configured toprojected the patterned radiation beam onto a target portion of thesubstrate; and a fluid handling system according to claim 18 configuredto provide an immersion liquid between the projection system and thesubstrate, or the substrate table, or both the substrate and thesubstrate table.
 20. A method of reducing a pressure fluctuation of animmersion liquid used in an immersion lithographic apparatus, the methodcomprising: extracting a two-phase fluid from a location in theimmersion lithographic apparatus using a fluid extraction system; andreducing a pressure fluctuation in the two-phase fluid by using aflexible boundary portion of the fluid extraction system, the flexibleboundary portion configured to change shape in response to a change inpressure differential across the flexible boundary portion.